Immunoprecipitations of RFP from human cells expressing RFP. Input (I), non-bound (FT) and bound (B) fractions were separated by SDS-PAGE followed by Coomassie staining and Western Blotting. The bound fraction of the conventional RFP antibodies shows in addition to RFP contaminating heavy chain and light chain. The bound fraction of the RFP-Trap® does not contain these contaminating polypeptide chains.